1. Field of the Invention
The present invention generally relates to a system for and its method of controlling handover, a mobile terminal, and an apparatus for controlling handover, and particularly relates to a system for and its method of controlling handover between homogeneous or heterogeneous wireless systems at the network side so as to enable a reduction in the throughput of the mobile terminal.
Furthermore, the present invention relates to the mobile terminal and the apparatus for controlling handover which are used in such a system for controlling handover.
2. Description of the Related Art
In recent years, the Wireless Local Area Network (WLAN) has been spreading rapidly and also has been watched with keen interest as means for connecting to the Internet.
In the WLAN, when changing on the move from one connecting access point to another, the IP address of the mobile terminal changes so that a problem of intermittent data flow arises in a case such as streaming. To this end, as a method of solving this problem, the “Mobile IP” has been proposed. In the Mobile IP, having a home address and an agent address enables the mobile terminal to retain connectivity even when the connecting access point changes from one to another.
Furthermore, although the transmission data rate of the WLAN is higher than that of a mobile telephone network, in order for the WLAN to achieve the same level of ease-of-use as the mobile telephone network, the problem of handover needs to be solved so as to be able to use the WLAN consistently without a break in data communications even when the mobile terminal is on the move. In order to respond to this problem, the Hierarchical Mobile IP (HMIP) which is based on the Mobile IP has been proposed. This HMIP enables the enhancement in the speed of handover as registration at the home agent is not performed every time a location is registered. More specifically, a server called the Mobility Anchor Point (MAP) having a function similar to that of the home agent is provided within a foreign network, and the location information is registered within the MAP so as to implement the enhancement in the handover speed.
Non-Patent Document 1
Hesham Soliman, Claude Castelluccia, Karim El-Malki, Ludovic Bellier, “Hierarchical MIPv6 mobility management”, Internet draft, draft-ietf-mobileip-hmipv6-03.txt., 2001
However, as seen in the HMIP described above, in the handover using the WLAN, the terminal itself needs to designate a route in the network. An IP (Internet Protocol)-centric network (the so-called IP network) is layered so that the own layer number and the IP address are provided as broadcast information to the terminal. At the terminal side, its own optimal route (which does not produce redundant routes) is determined using the broadcast information.
Now it is expected that, in the next generation mobile telephone system which follows the current mobile telephone system, a wide variety of wireless systems including the mobile telephone and the WLAN systems will be interconnected via the IP network. For example, in the case of accommodating such a wide variety of wireless systems in a common IP network, the development of handover technology to seamlessly connect the wide variety of wireless systems in response to the location and the taste of the user, the communications content, etc., will become quite important.
Furthermore, at the terminal side, although study on a software-defined radio that enables the handling of a variety of wireless methods and protocols is underway, it is expected that the amount of processing at the terminal side will increase in order to achieve such greater functionality. Therefore, if the HMIP of the Mobile IP as described above is implemented as it is in the software-defined radio, a problem arises such that there will be a further increase in the amount of processing at the terminal so as to make minituarization difficult.